This invention relates to a linear driving mechanism which is provided in an electronic components mounting apparatus such as an electronic component placement machine, and linearly drives a driven member such as a mounting head by a linear motor.
In electronic components mounting apparatuses such as an electronic components placement machine, a linear driving mechanism has been extensively used as an elemental mechanism forming a head-moving mechanism for moving an operating head such as a mounting head. In recent years, instead of a conventional linear driving mechanism of the type in which a rotational motion of a motor is converted into a linear motion by a ball screw, there has been used the type of linear driving mechanism in which a linear motion is directly effected by a linear motor (see, for example, JP-A-2002-299896). By adopting this type, there is achieved the linear driving mechanism capable of effecting a high-speed operation with high positional accuracy.
A linear motor is of such a type that a magnetic force is produced between a stator, mounted in a driving direction, and a moving element disposed in opposed relation to the stator, thereby obtaining a driving force. Therefore, the moving element is always kept in a heated condition by a drive current. Therefore, heat is transferred from the moving element to a drive transmission portion interconnecting a driven member and the moving element, and is further transferred to the driven member, so that the temperature of this driven member rises. When the driven member is subjected to thermal expansion and contraction because of this temperature rise, there has been encountered a problem that various troubles, such as lowered precision of positioning of the operating head mounted on the driven member, are incurred.